The UserFrosting Framework contains the critical services required for UserFrosting to work. This is the only part of UserFrosting that is not considered a sprinkle. The reason for it not being considered a sprinkle is simple : the Framework contains the code required for the Sprinkle system to work. If it was a sprinkle itself, we'd be in a loop!
Aside from managing sprinkles (through the cleverly named SprinkleManager), the Framework is responsible for setting up the Slim/Symfony Console application and initiating the PHP-DI container.
The UserFrosting Framework also contains some parts that are not tied directly to UserFrosting. These parts could be used outside of UserFrosting, in a completely separate application.
The documentation for each part is embedded in the next chapters, but you can still see each part's documentation on it's own :